Not since microwave radio has there been as significant a technology developed in telecommunications as lightwave technology which is manifested in the use of fiber lightguides. Optical or lightguide fibers are inherently versatile as a transmission medium, all forms of information be it voice, video or data can be carried on a fiber lightguide. Also, lightwave systems are ideally suited to the high bandwidth requirement of digital transmission and hence are well-matched to the evolving transmission network in this country.
The medium for lightwave transmission is glass, a solid whose structure is amorphous or random, as opposed to the crystalline structure that normally results when molten materials solidify. Fibers for lightwave communications are drawn from a preform--an elongated cylinder of glass having an inner core and an outer cladding--with the thickness of the core and the cladding being in the same ratio in the fiber as they are in the preform. A drawing system is well-described in an article by D. H. Smithgall and D. L. Myers in the winter 1980 issue of the Western Electric Engineer.
In the drawing system, the preform is fed into a heated region where it necks down to the fiber size as the fiber is pulled from the heat zone. The diameter is measured at a point shortly after the fiber is formed, and this measured value is input to a control system. Within the controller, the measured fiber diameter is compared to a desired value and an output signal is generated to adjust the draw speed such that the fiber diameter approaches the desired value. After the fiber diameter is measured, a protective coating is applied and the material is cured on the fiber.
The drawn fiber is taken up on a lightweight, plastic spool such that end portions of the fiber on each spool are available for testing. The spools of drawn, tested fiber are subsequently used to supply ribbon and/or cabling apparatus.
The winding parameters during takeup must be carefully controlled; collection at low tension is necessary in order to minimize the damage to the fiber or a coating thereon and reduce the effect of microbending loss on transmission measurement. Therefore, the winding tension is minimized and the distribution of fiber across a spool is controlled to facilitate unwinding at a subsequent operation.
The control fiber tension, the fiber is allowed to form a catenary between the capstan and the take-up. As the spool fills, the catenary tends to decrease in length and it becomes necessary to decrease take-up motor speed under controlled conditions. This is accomplished with an electro-optical system including a closed circuit television camera which detects any change in the height of the fiber catenary and causes changes in the take-up motor speed. This arrangement is described in commonly assigned application Ser. No. 040,026 filed on May 18, 1979 in the name of R. E. Frazee, Jr.
In addition to the problem of correlating the rotation of the takeup spool, a problem has been the uninterrupted takeup of all the fiber that can be drawn from a preform. Since the spools currently in use will each hold only a fraction of the total product output of a single preform, an operator must manually make a cutover between spools supported on a common axis, which introduces additional handling and possibly delay time in the takeup.
Widespread use of lightguide fiber cables will require that economies must be introduced into present manufacturing processes. It would be desirable, for example, that the drawing of a preform and its takeup be accomplished so that all the fiber drawn from a single preform is taken up without interruption and with a minimum of handling.
Further, the manufacture of lightguide fiber requires the use of sophisticated testing procedures at each step in order to insure a lightguide fiber of the highest quality. In order to accomplish this at takeup, it is necessary that the end of the lightguide fiber which initially engages a spool, as well as the final end portion on a spool, be accessible so that test apparatus can be connected thereto to facilitate testing during takeup.
While the prior art is replete with patents that disclose takeups particularly for copper based conductors, there is no known takeup which is ideally suited for taking up lightguide fiber. Such a system must include provisions for accessing an inner end of the lightguide package and must provide for continuous uninterrupted takeup while being capable of being controlled to avoid undue stressing of the lightguide fiber as it is taken up.
In the prior art, Bonzo et al in U.S. Pat. No. 4,138,069 shows a tangential cutover type of takeup apparatus for glass optical filaments in which a plurality of spools are mounted rotatably on parallel axes projecting from a turret so that as one spool is wound full, it is moved out of a takeup position, the filament is attached to an empty spool which is moved into the takeup position, and the filament is severed from the full spool. Each of the spools is constructed with one flange having a rubber extension which includes two humps with a rubber O-ring disposed between the humps. Since a roller is used to depress a hump away from the O-ring to form a gap into which the filament falls and is gripped when the roller is disengaged, the timing during cutover is critical in order to form the gap and input the filament. The prior art also includes U.S. Pat. No. 2,893,652 which shows a common axis takeup arrangement in which a flange of a reel includes a generally V-shaped groove and one or more angularly spaced detents on the flange to catch wound stock if some should escape from the groove and tend to unwind. In another common axis arrangement, a spool flange is provided with a groove in the flange which extends across a chord of the flange tangent to the spool hub and into which groove a length of wire extending from a snagger at cutover is forced. Because of the impact that a snagger has on an elongated material being taken up at cutover, the use of a snagger to capture drawn lightguide fiber is not preferred.
What is needed is a drawn lightguide fiber takeup apparatus which is specially suited to the handling of this kind of material without abuse, which is uncomplicated and which provides a takeup package in which the leading end of the fiber on a spool is accessible for testing. The length of the accessible leading end must not be so long that it whips about the spool during takeup causing damage to the other convolutions.